Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies. UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the Node-B's and Radio Network Controllers which make up the UMTS radio access network. This communications network can carry many traffic types from real-time Circuit Switched to IP based Packet Switched. The UTRAN allows connectivity between the UE (user equipment) and the core network. The UTRAN contains the base stations, which are called Node Bs, and Radio Network Controllers (RNC). The RNC provides control functionalities for one or more Node Bs. A Node B and an RNC can be the same device, although typical implementations have a separate RNC located in a central office serving multiple Node B's. Despite the fact that they do not have to be physically separated, there is a logical interface between them known as the Iub. The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). There can be more than one RNS present in an UTRAN.
3GPP LTE (Long Term Evolution) is the name given to a project within the Third Generation Partnership Project (3GPP) to improve the UMTS mobile phone standard to cope with future requirements. Goals include improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with other open standards. The LTE project is not a standard, but it will result in the new evolved release 8 of the UMTS standard, including mostly or wholly extensions and modifications of the UMTS system.
In most orthogonal systems with Automatic Repeat (ARQ), the uplink (UL) acknowledgement (ACK) is implicitly mapped on corresponding time/frequency/code resources depending on the downlink (DL) packet location in time/freq/code. The one-to-one mapping is usually linked to each minimum allocation of virtual resource block (VRB), with each packet containing multiple VRBs. This implies that for each packet, a user equipment (UE) has several instances of ACKs available for transmission (reserved resources), one corresponding to each VRB contained within the packet. This may lead to large overheads, especially when the packets span multiple VRBs. For instance, with one cyclic shift in pre-assigned UL physical resource block (PRB) per DL VRB. Considering Six ACKs per UL PRB, an overhead on the DL can be shown to be 16.66%.
It has been suggested that one cyclic shift and resource block combination can be implicitly mapped per physical downlink control channel (PDCCH). Thus, the UL overhead would be dictated by the number of DL assignments, which would entail 16.66% for 1.25 MHz and 4% for larger bandwidths, assuming (4, 8, 16) DL PDCCH for (5, 10, 20) MHz. However, this approach suggests that each packet has to be scheduled, shifting overhead from the UL to the DL. This approach would not be appropriate for control-less operation. Every Voice Over IP (VoIP) packet would be scheduled by the PDCCH in a unicast manner. Should the PDCCH be addressed to multiple users by bitmap (i.e., group PDCCH) for VoIP, this approach would not work. This approach does not work for persistent assignments, at least it is believed not without cumbersome modifications.